The United Nations kicked off the first World Population Day on July 11, 1987. World population has risen from 2.5 billion in 1950 to 7 billion later this year. The United Nations released its latest population projections [PDF] back in May:
The high projection variant, whose fertility is just half a child above that in the medium variant, produces a world population of 10.6 billion in 2050 and 15.8 billion in 2100. The low variant, whose fertility remains half a child below that of the medium, produces a population that reaches 8.1 billion in 2050 and declines towards the second half of this century to reach 6.2 billion in 2100. For long-term trends the medium variant is taken as reference.
The medium-variant projection for 2050 is more certain than for 2100 because people who will be 40 years and older in 2050 are already born. According to the medium variant, it will take 13 years to add the eighth billion, 18 years to add the ninth billion and 40 years to reach the tenth billion.
High fertility is associated with lower life expectancies. The U.N. report notes that the highest fertility countries have an average life expectancy of just 56 years. The good news is that the U.N. expects that life expectancies among high-fertility countries to rise to 69 years in 2045-2050 and to 77 in 2095-2100. Total fertility rates plummet [PDF] when women can expect to live more than 60 years. Improving life expectancy trends could put the world population on the lower variant trend toward a population peak in 2050 with a decline thereafter.
World Population Day Bonus: Researchers at Oregon State University have helpfully calculated the carbon legacy [PDF] that breeders leave behind with each additional child:
Under current conditions in the United States, for example, each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female, which is 5.7 times her lifetime emissions. A person's reproductive choices must be considered along with his day-today activities when assessing his ultimate impact on the global environment.
As someone who is voluntarily childless, where do I pick up my carbon credits? At say, $50 per ton, that would come to nearly $500,000 per forgone child.
For more background see my columns, "The Invisible Hand of Population Control," and "Why Are People Having Fewer Kids?" (BTW, the answer to the question in the second column is it's because they don't like them very much.)